A Bacteriophage is any one of a number of virus-like agents that infect bacteria and the term is commonly used in its shortened form, ‘phage’. Bacteriophages consist of an outer protein hull enclosing genetic material. The genetic material can be single stranded or double stranded DNA or RNA. To survive, bacteriophages need a host and every bacterium has a specific partner phage. When the bacteriophage invades into a host, it duplicates itself and then induces expressions of enzymes involved in the decomposition of cell wall of the host cell. The enzymes destroy the cell wall by attacking murein or peptidoglycan which is responsible for rigidity and mechanical strength of the cell wall.
The bacteriophage was first found by Twort, an English bacteriologist, in 1915 during his research on the phenomenon that micrococcus colony is decomposed opaque by something. And in 1917, a French bacteriologist d'Herelle found out that there was something that decomposes Shigella disentriae in filtrate of feces of a patient with dysentery, and he continued to study to identify the material, leading to the finding of the bacteriophage which means “eating bacteria”. Since then, bacteriophages had been continuously identified specific to various pathogenic bacteria including Shigella, typhoid bacillus and comma bacillus. Dr. Delbruck of Cal-tech and some European scientists who had moved to USA during World War II focused their studies on the bacteriophage specific to E. coli. Since penicillin was discovered by Flemming in 1950, the antibiotic has been used widely and the research on bacteriophages has been limited to some Eastern European countries. However, multi-drug resistant pathogenic bacteria have been frequently reported since 2000, which must be resulted from the abuse and misuse of antibiotics. Based on its potential for alternative antibiotics, bacteriophages have been now in the center of the studies.
Even though antibiotics (or antibacterial agents) are still major therapeutic agents for the treatment of various infectious diseases, the antibiotics-based treatment has a serious problem. Numbers of multi-drug resistant strains have been found since 1980s, and it may be due to the excessive use of such antibiotics. In 1986, Staphylococcus aureus having resistance against vancomycin, which is so called ‘the last antibiotic’, and other multi-drug resistant strains were found, giving a great shock to those in medical field. Vancomycin resistant enterococci (VRE) was first reported in France in 1986 and first separated in USA in 1988. Since then, the cases of Enterococci infection have been increased every year with high frequency, everywhere including Europe, USA, Singapore, Japan, Australia, Korea, etc, making the vancomycin resistant Enterococci as a causal agent of nosocomial infections. In Korea, VRE was first isolated in 1992. Therefore, it is an urgent request to develop a novel antibiotic to treat the conventional antibiotic resistant bacteria and further to lead national health and medical techniques. To achieve the above goal, a novel antibiotic has to be developed through the completely different method.
Again, it is urgently required to develop an alternative antibiotic to solve the problems of multi-drug resistant bacteria along with the abuse or misuse of the conventional antibiotics and the residual antibiotics.
Thus, the present inventors isolated a novel bacteriophage having killing activity specific to Staphylococcus aureus and deposited it at Korean Agricultural Culture Collection (KACC), National Institute of Agricultural Biotechnology (NIAB) on Jun. 14, 2006 (Accession No: KACC 97001P). Although this novel bacteriophage is very effective for the prevention and treatment of infectious disease caused by Staphylococcus aureus, the use of this bacteriophage has some defects. So, it is required to develop a novel material that improves safety of its use in various fields related to the selective killing Staphylococcus aureus. 
The present inventors completed this invention by providing a novel antimicrobial protein having killing activity specific to Staphylococcus aureus, which was derived from the bacteriophage discovered by the present inventors, and further by confirming that this novel antimicrobial protein specific to Staphylococcus aureus can be effectively used for the prevention and treatment of disease caused by Staphylococcus aureus. 